Switching device actuated by a transponder

ABSTRACT

Proposed is a device actuated by a transponder for the generation of a switch signal. The device is based on an oscillating circuit ( 10 ) with a capacitance (C 1 ), an identification coil (L 1 ) and an oscillator amplifier ( 12 ). Connected to the oscillating circuit ( 10 ) is a frequency observer ( 20 ) which evaluates the frequency (f 1 ) tuned in the oscillating circuit ( 10 ) and which when finding a change emits a switch signal (S). A change of the frequency in the oscillating circuit ( 10 ) is effected by the approach of a transponder ( 60 ). The device permits a nearly loadless transponder identification.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Phase of International Application Ser.No. PCT/EP03/01144, filed Feb. 5, 2003.

FIELD OF THE INVENTION

The invention starts out from a device of the species of the main claim.A device of this kind is known from DE 198 55 207 C1. Therein atransponder reading apparatus is described which can be switched on by aswitch signal generated by bringing near a ferromagnetic element to anidentification coil so as to induce a voltage in the latter. Theidentification coil is provided specifically for triggering theswitching process and is formed around a permanent magnet. Theferromagnetic element together with the transponder is placed on a codecarrier which can be for example a key. The device permits thetransponder reading apparatus to be switched on by the mere approach ofthe code carrier without this code carrier having to possess an ownpower supply. The device requires the continuous operation of anamplifying circuit used for the amplification of the voltage induced inthe identification coil. Here no-load operation losses do arise whichhave to be continuously equalized by the power supply. The operation ofthe device therefore requires a sufficiently large power supply. If thepower supply has to be dimensioned very small, the device cannot be usedor only with restrictions.

DESCRIPTION OF THE BACKGROUND ART

One widespread transponder application are contactless portable datacarriers which cooperate with a reading device that contains a coil,with the help of which the reading device performs the power supply forthe transponder brought into the response range and the readout. As tobe able to identify the bringing near of a transponder the readingdevice cyclically at short time intervals produces a magnetic fieldwhich is suitable for supplying a transponder with power that,optionally, is brought within the addressing range. At the same time thereading device usually sends out one interrogation signal at a time withwhich a transponder is addressed. The regular production of magneticfield and interrogation signal causes a comparatively high energyconsumption which renders the concept unsuitable for applications inwhich a sufficiently large power supply cannot be made available.

Furthermore, in DE 100 06 747 A1 can be seen a generic device whichespecially deals with the problem of power consumption. It is proposedto equip a portable transponder element with a permanent magnet whichwhen approached to a reading apparatus actuates a switch disposedtherein that is controlled by a magnet. The proposed device minimizesthe power consumption of the reading apparatus since the latter canremain completely switched off during the absence of a transponder. Theinstallation of a permanent magnet requires constructional measuresregarding the transponder elements to be equipped with such a magnet,and such measures cannot always be taken easily. The mechanicintegration is problem enough as to render the solution not suitablefor, for example, contactless chip cards. Furthermore, the magneticfield produced by a permanent magnet often is undesirable with regard tothe practical usability of the transponders equipped with such permanentmagnets. This applies for example to portable data carriers in chip cardformat where information is stored on a magnetic stripe. The handling ofsuch transponders is also restricted in so far as they have to be keptaway from other circuits sensitive to magnetic fields.

The book “RFID-Handbuch” written by K. Finkenzeller, Carl Hanser Verlag,2nd edition, 2000, describes in detail the basic principles of thetransponder technology and shows examples of transponder applications.In particular chapter 4 of this book gives basic information andadditional explanations to the invention described hereinafter. Explicitreference is made to these passages in particular and to the book as awhole, they shall be part of this application.

From DE 196 02 316 C1 there is known a device for the transmission ofdata and supply power from/to a transponder which can be used forexample in a theft protection system of a motor vehicle. The device hasa fixed transceiver as well as a portable transponder which whenapproached to the transceiver cooperates with it. To achieve a power ordata transmission as effective as possible it is proposed after themanufacturing of the transceiver to adjust the resonant frequency in thetransmitting antenna circuit and/or the quantity of the exciting currentflowing in the transmitting antenna circuit in such a manner that theresult is a maximum power transmission to the transponder. The foundadjustment is fixed by circuit-technical means.

From DE 199 23 367 A1 a device for the non-contacting position recordingof an object is known which has a transmitting antenna, a receivingantenna and an evaluation circuit. Here transmitting antenna andreceiving antenna influence each other. With the presence of an objecttheir coupling changes. The change is recorded and evaluated.

SUMMARY OF THE INVENTION

It is the problem of the invention to specify a switching deviceactuated by a transponder which enables a power consumption as low aspossible within the connected circuit and at the same time unrestricteduse.

This problem is solved by a device with features of the main claim.According to the invention the generation of a switch signal and withthat a switching process is triggered upon detection of the detuning ofthe resonant frequency of an oscillating circuit. The oscillatingcircuit and the circuit required for the identification can be operatednearly loadless. Accordingly, the inventive switching device shows anextraordinarily low power consumption. Therefore, it is especiallysuitable for the actuating of circuits, the power supply of which comesfrom a limited power source. In particular it is suitable for supplyingcircuits powered by small batteries. Since the device is to a far extendindependent of the size of the provided power source, a flexible use ina multitude of installation places is possible for which the deviceotherwise would not be suitable. The device is suitable, inter alia, forinstalling in door locking apparatus, so as to enable atransponder-aided, non-contacting opening of the door.

Furthermore, the inventive device is very user-friendly because itrequires no special handling at all on the part of the user. Thetransponders used have a conventional form of appearance and are used inthe conventional way. The conventional design of the transponders usedalso has an advantageous effect on their manufacturing since specialconstructional measures regarding the structure are not required. Onefurther advantage of the inventive device in particular is the fact thatthe coil which is already present in the transponder triggers theswitching and therefore special components in the transponder are notrequired. Accordingly, the transponders can be of a cost-effectivedesign.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the figure one embodiment of the invention isdescribed in more detail in the following.

Figure:

FIG. 1 shows a block diagram of a switching device,

FIG. 2 shows an equivalent diagram of a part of the switching device,

FIG. 3 shows an equivalent diagram of a frequency observer,

FIG. 4 shows one application of the switching device in a door lockingapparatus.

DESCRIPTION DETAILED DESCRIPTION OF THE INVENTION

The basic elements of the switching device shown in FIG. 1 are anoscillating circuit 10, a frequency observer 20 connected to theoscillating circuit 10, a switch 30 disposed in the oscillating circuit10 and actuated by the frequency observer 20, a function circuit 40connected to the switch 30 and the frequency observer 20 as well as atransponder 60 for triggering the switching process. A further basicelement is a power source 50 which supplies the oscillating circuit 10,the frequency observer 20 and the switch 30 with power.

The oscillating circuit 10 is composed of an identification coil L₁, acapacitance C₁, and an oscillator amplifier 12. A further component ofthe oscillating circuit 10 is the switch 30. The identification coil L₁and the capacitance C₁ determine the resonant frequency f₁ of theoscillating circuit 10. The oscillator amplifier 12 expediently has theform of a feedback coupling transistor amplifier. It keeps theoscillating circuit 10 in tune to the resonant frequency f₁ andequalizes the arising power losses caused by the identification coil L₁and the capacitance C₁, as well as, if any, further present components.For this purpose it is connected to the power source 50.

The frequency observer 20 contains a circuit which allows theidentification of changes in the resonant frequency f₁ tuned in theoscillating circuit 10. For this purpose the circuit is preferablyformed as an amplitude sensing element, as a phase sensing element or asa frequency sensing element. When the frequency observer 20 identifies adetuning of the resonant frequency f₁ in the oscillating circuit 10 itgenerates a switch signal S which addresses via a control line 22 theswitch 30 and the function circuit 40.

The power supply of the frequency observer 20 is effected by the powersource 50 the frequency observer is connected to for this purpose. Thisconnection is expediently effected via a switch 24 which is actuated bythe function circuit 40. Having been switched on by a switch signal Sthe function circuit 40 by means of the switch 24 disconnects thefrequency observer 20 from the power supply 50 for the period of timethe communication with a transponder 60 lasts. Upon completion of acommunication with a transponder 60 the function circuit 40 switches onthe frequency observer 20 by means of reconnecting it with the powersource 50 by activating the switch 24.

The switch 30 can be of any constructional type. In its normal position32 it closes the oscillating circuit 10 as outlined in FIG. 1. Havingreceived a switch signal S via the control line 22 it changes into theposition 34 and connects the identification coil L₁ with the functioncircuit 40.

The function circuit 40 in principle can be formed by any circuit whichcan be addressed by a switch signal S. In the embodiment it is assumedthat the function circuit 40 is a transponder reading device workingcontactlessly which after a communication with a transponder 60 eithertriggers or not triggers a function. In view of the advantagesachievable by means of the described device it is furthermore assumedthat the function circuit 40, in the following referred to as readingdevice, has an own power source 42 in the form of a battery. Forcarrying out a communication with a transponder 60 the reading device 40is connectable to the identification coil L₁ by moving the switch 30into the position 34. It is switched on by a control signal S suppliedvia the control line 22. Furthermore, the reading device 40 can beconnected to a switch 24 disposed between power source 50 and frequencyobserver 20 through which the frequency observer 20 can be switched onand off by either being connected or being not connected to the powersource 50.

The power source 50 expediently has the form of a battery. It effectsthe power supply for the oscillator amplifier 12, the frequency observer20 and the switch 30. The power source 50 can form a constructional unitwith the power source 42 and in particular can also be formed by asingle power source such as a single battery.

The transponder 60 is of a conventional constructional type and acts,for example, as a carrier of a code which is verified by the readingdevice 40. For example it has the form of a portable data carrier in theformat of a standard chip card. But it can also be of any otherconstructional design, such as a wristwatch or a writing implement.Essential component of the transponder 60 in view of the devicedescribed herein is a transponder coil L₂. By means of such atransponder coil a switching process can be triggered.

The basic function of the device described in FIG. 1 is a magneticreverse coupling M which occurs between identification coil L₁ andtransponder coil L₂, if the two are brought into sufficient proximity toeach other. The reverse coupling M here occurs without an activeinvolvement of the transponder 60, the transponder 60 does not need tosupply energy. By means of the reverse coupling M an impedance ZT istransformed in the identification coil L₁. The coupling of the impedanceZT leads to a change in the resonance conditions in the oscillatingcircuit 10. The result is a change in the resonant frequency f₁ of theoscillating circuit 10. Here the coupled impedance ZT is not dependenton the quantity of the current I₁ flowing in the oscillating circuit 10.Therefore, the current can be adjusted to a value of nearly 0 when thecomponents of the oscillating circuit are suitably dimensioned.

To the coupled impedance ZT the following appliesZ _(T)=ω² k ² L ₁ L ₂(R ₂ +jωL ₂ +R _(L)/(1+jωR _(L) C ₂))⁻¹  (1)

while for the magnetic coupling M between identification coil L₁ andtransponder coil L₂ appliesM=k(L ₁ L ₂)^(1/2.)

A derivation of the relation (1) for the transformed impedance Z_(T) canbe found in “RFID-Handbuch”, K. Finkenzeller, 2nd edition, 2000, inparticular chapter 4.1.10 already mentioned in the introduction.Especially referring to this book, from a detailed derivation isrefrained at this point.

As to explain the meaning of the relation (1) FIG. 2 shows an equivalentdiagram of the oscillating circuit 10 and the transponder 60. Theoscillating circuit 10 comprises the identification coil L₁, an ohmicresistance R₁ assigned to the identification coil L₁, a feedbackcoupling amplifier V as oscillator amplifier 12, as well as a totalcapacitance C₁ which consists of a first partial capacitance C₁₁ tocause a division of the voltage for the feedback coupling, as well as asecond partial capacitance C₁₂ for tuning the resonant frequency. Thecomponents of the oscillating circuit 10 are preferably dimensioned insuch a manner that the identification coil L₁ and the capacitance C₁ toa large extend alone determine the resonant frequency f₁ of theoscillating circuit 10.

As to achieve an effect as large as possible L₁ and C₁ are preferablychosen in such a manner that the off-load oscillating circuit 10 worksexactly on the resonant frequency of a corresponding transponder 60. Inthis case a maximum value is achieved for ZT, as a result of which theidentification of a detuning by the frequency observer 20 is improved.

Following usual transponder solutions typical resonant frequencies f₁tuned in the oscillating circuit 10 and also used by the transponder 60range below 135 kHz. But in principle any other frequency ranges arealso suitable, e.g. the frequency of 13.56 MHz relevant for ISOstandards.

The transponder 60 consists of the transponder coil L₂, a voltage sourceU₂, a transponder impedance Z₂, and an ohmic resistance R₂ of thetransponder coil L₂. The transponder impedance Z₂ is composed of a loadresistor R_(L) and a capacitance C₂. The voltage source U₂ generates thevoltage which is induced due to the magnetic coupling M in thetransponder coil L₂ by the current I₁ flowing in the identification coilL₁.

FIG. 3 shows an equivalent diagram of a possible frequency observer 20.It is connected to the oscillating circuit 10 at one of the connectingpoints A. The basis of the shown frequency observer 20 is formed by adifferentiating circuit which comprises a diode D₃, a differentiatingcapacitance C₃₁ connected in series, as well as a parallel circuitconsisting of a resistance R₃ and a capacitance C₃₂ through which theoutput of the diode D₃ is connected to ground. The output of thedifferentiating capacitance C₃₁ forms the input of a Schmitt triggercircuit ST, to the output of which an optionally generated signal ispresented.

The frequency observer 20 with the circuit depicted in FIG. 3 works asfollows. If the off-load oscillating circuit 10 in the absence of atransponder 60 is tuned to a constant oscillation with resonantfrequency f₁, to the output of the diode D₃ will be applied a constantdirect voltage which is proportional to the amplitude of the oscillationin the oscillating circuit 10. Via the resistance RB it producesa—minimal—current flow I₃, the quantity of which can be adjusted to avalue of nearly 0 by a respective dimensioning of the resistance R₃.

If a transponder 60 with a transponder coil L₂ is moved into the fieldof the identification coil L₁, this approach will effect the coupling ofan impedance ZT in the oscillating circuit 10 according to the relation(1). Because of this the resonant frequency f₁ and the amplitude of theoscillation in the oscillating circuit 10 change. This temporarilyresults in an alternating voltage at the output of the diode D₃ whichchanges in accordance with the change in the amplitude, this alternatingvoltage appears at the differentiating capacitance CB as voltage pulseand effects a short-term impulsive current flow to the Schmitt triggercircuit ST. The voltage pulse causes the Schmitt trigger circuit to emita switch signal S. The switch signal S now on the one hand effects theswitching of the switch 30 to position 34. As a result of this theidentification coil L is connected to the reading device 40 andsubsequently serves the latter as a power transmitter and communicationapparatus for the power supply and communication with the transponder60. On the other hand the switch signal S switches on the reading device40.

If a switch 24 exists, the reading device 40, after having been switchedon itself, switches off the frequency observer 20 by turning the switch24 into the position 28. Afterwards the reading device 40 communicatesvia the coil L₁ with the transponder 60. Upon completion of thecommunication with a transponder 60 the reading device 40 switches onthe frequency observer 20 again.

FIG. 4 shows an application of the described switching device in alocking system for doors. A rotatable door knob 70 is depicted which ismounted on a shaft 72 that leads into a door—not shown—and there bymeans of rotation the shaft enables the unlocking or locking of the doorby moving a mechanic interlock means. The door knob 70 inside has afirst hollow space 74 for accommodating a first battery 50 whichsupplies the switching device with power and a second battery 42 whichsupplies a—not shown—reading device 40 with power. Instead of twobatteries 50, 42 a single battery can also be provided which suppliesthe switching device as well as the reading device 40. Furthermore, onthe outer end face facing the user the door knob 70 has a second hollowspace 76 wherein an identification coil L₁ is disposed. Theidentification coil L₁ according to the variation depicted in FIG. 1 isconnected to the reading device 40 via a—also not shown—switch 30 andafter the identification of a transponder 60 it serves for thecommunication with the latter as well as for its power supply.

The door knob 70 is made of a metallic material. As to ensure that theoperation of the identification coil 76 is not hindered by losses due toeddy current induction in the door knob material the inner surface ofthe hollow space 76 is covered with a shielding 78. Suitable materialsfor the shielding 78 are e.g. ferrite materials or highly permeablemetals such as amorphous metals. Furthermore, it can be provided thatthe identification coil 76 is winded on a ferrite core. This embodimentis particularly advisable in case the resonant frequency f₁ in theoff-load oscillating circuit 10 is lower than 135 kHz.

In a further, not shown hollow space in the door knob 70 is disposed thereading device 40. As shown in FIG. 1 the reading device 40 for thecommunication with a transponder 60 preferably uses the identificationcoil L₁ which for this purpose after the identified approach of atransponder 60 is switched via a switch 30 to the reading device 40.

Observing the basic principles of realising a switching device actuatedby means of the identification of the detuning of a resonant frequencyf₁ in a nearly loadlessly operated oscillating circuit 10, theprescribed switching device allows a multitude of designs. This appliesto the constructional realisation of the oscillating circuit 10 and thefrequency observer 20. The latter in particular can be replaced by anyother circuit that permits an observation of the resonance conditions inan oscillating circuit and the changes thereof while consuming a poweramount as small as possible. Among other things the frequency observer20 can be realised using for example a pulse generator such as amonoflop with an output pulse of constant time to which an integratorand a threshold switch are connected in series. A further possibleembodiment contains a bandpass filter matched with the resonantfrequency f₁ to which a rectifier circuit as well as a threshold switchare connected in series. It is also thinkable to provide only arectifier circuit to which a threshold switch or a window discriminatoris connected in series. In the oscillating circuit 10 the tapping of thefeedback coupling of the amplifier can be effected at other suitablepoints, e.g. via the coil. Furthermore, it is not required that theidentification coil L₁ after addressing the frequency observer 20 via aswitch 30 is connected to the reading device 40. It can also be providedthat the reading device 40 is equipped with an own coil and a switchsignal S optionally transmitted by the frequency observer 20 directlyswitches on the reading device 40. A switch 30 is omitted in thisembodiment. For the switch 24 a multitude of realisation possibilitiesare suitable. It can be realised, for example, within the frequencyobserver 20 and it is addressed via the signal line 22. Furthermore, theuse of the proposed switching device is not restricted to theapplication in door locking systems as described by way of example. Thedevice is rather suitable for any other switching situations.

1. A switching device actuated by a transponder for the generation of a switch signal, comprising: an oscillating circuit with a capacitance; an identification coil; and an oscillator amplifier; wherein the identification coil and the capacitance determine the resonant frequency of the oscillating circuit, a frequency observer which evaluates the frequency tuned in the oscillating circuit and which when finding a change compared with an off-load state generates a switch signal, and wherein said device further comprising a switch which either closes the oscillating circuit or connects a function circuit to the identification circuit, said function circuit being formed by any circuit which can be activated by the switch signal.
 2. A switching device according to claim 1 characterized in that the switch signal is led via a control line to the function circuit.
 3. A switching device according to claim 1 characterized in that the oscillator amplifier and the frequency observer are supplied with power by an independent power source.
 4. A switching device according to claim 3 characterized in that the frequency observer is separably connected to the power supply.
 5. A switching device according to claim 4 characterized in that the separability is realised by means of the switch which is actuated by the function circuit.
 6. A switching device according to claim 1 characterized in that the switch can be actuated by the switch signal of the frequency observer.
 7. A switching device according to claim 1 characterized in that the resonant frequency of the oscillating circuit is defined by the identification coil and a capacitance which is connected to the oscillating circuit for this purpose.
 8. A switching device according to claim 1 characterized in that the resonant frequency of the oscillating circuit coincides with the resonant frequency of a transponder.
 9. A switching device according to claim 1 characterized in that the frequency observer contains a differentiating circuit.
 10. A switching device according to claim 1 characterized in that the frequency observer is formed as to identify a change in the phase relationship of the resonance oscillation tuned in the oscillating circuit.
 11. A method for switching on a function circuit, comprising utilizing a switching device according to claim
 1. 12. A method according to claim 11, characterized in that the function circuit is supplied with power by a limited power source.
 13. A system triggering a function with a function circuit which can be switched on by a switch signal characterized in that the generation of the switch signal is effected by a switching device according to claim
 1. 14. A system identifying an authorization with a transponder reading device which verifies the authorization of a user by communication and by means of a transponder characterized in that the transponder reading device is connected to a switching device according to claim 1 which switches on the transponder reading device when a transponder has been presented to it.
 15. A locking system for a door characterized in that it has a switching device according to claim 1 which switches on, by communication with a transponder, a transponder reading device that verifies the authorization of a user to actuate the locking system.
 16. A locking system according to claim 15 characterized in that the identification coil is disposed in a door knob.
 17. A locking system according to claim 15, characterized in that the identification coil is disposed in a hollow space, the inside surfaces towards the door knob of which are covered with a shielding.
 18. A locking system according to claim 15 characterized in that the shielding is made of a material that prevents losses caused by eddy currents induced in the door knob material. 